Wraparound spectacles whose lenses wrap around the eyes and the area close to both sides of the face are proposed to be used as sporting spectacles, sunglass and the like. By using the wraparound spectacles, many advantages can be achieved such as obtaining a wide vision, keeping the wind out from the eyes, and controlling incident light from the lateral direction. Thus, growing demand for the wraparound spectacles comes not only from the sports lovers, but also from the persons engaged in various outdoor activities. Further, there is another growing demand of the wraparound spectacles derived from functionality.
FIG. 22 is a perspective view showing an example of a spectacle frame 3 for configuring a pair of wraparound spectacles, and FIG. 23 is a plan view of the spectacle frame 3 viewed from above. The spectacle frame 3 includes a front 7, and two temples 8 respectively connected to the left and right ends of the front 7. The front 7 includes left and right rims 5 for holding the lenses, a bridge 9 for connecting the left and right rims 5, and a pad (nose pad) 4 attached to the inner side of the left and right rims 5.
Further, the left and right lens frame shapes 6, which are respectively the inner periphery shapes of the left and right rims 5, respectively correspond to the left and right lens shapes of the lenses fitted into the spectacle frame 3.
As can be known from FIGS. 22 and 23 that, in the wraparound spectacle frame 3, since the front 7 is largely curved along the face of the spectacle wearer, the front 7 has a very large front angle. A front angle θf is defined as an angle in the horizontal direction between a plane Ff of the front 7 (also referred to as “spectacle plane” hereinafter) of the spectacle frame and a plane Fs of each of the left and right lens shapes (referred to as “lens plane” hereinafter). In the present specification, the spectacle plane Ff is a vertical plane passing through the left and right lens shape centers (each lens shape center being an intersection of the horizontal centerline and the vertical centerline of a rectangle formed by two horizontal lines and two vertical lines circumscribing the lens shape) 2, and the lens plane Fs is a vertical plane passing through the horizontal centerline Lhc of each lens shape (i.e., the horizontal centerline of the rectangle formed by two horizontal lines and two vertical lines circumscribing the lens shape). For most wraparound spectacle frames described above, the front angle θf is typically set in a range from 10 to 30 degrees.
Conventionally, spectacle lenses with no dioptric power (also referred to as “plano lenses” hereinafter) have been used as the spectacle lenses to be fitted into the aforesaid wraparound spectacle frame; however, in recent years, single-vision spectacle lenses, which are spectacle lenses with dioptric power (also referred to as “prescribed lenses” hereinafter), are also used as the spectacle lenses to be fitted into the aforesaid wraparound spectacle frame. However, if single-vision spectacle lenses (prescribed lenses) designed without considering the front angle is simply fitted into a spectacle frame having large front angle, such as the aforesaid wraparound spectacle frame, since prismatic effect, astigmatism and mean power error (also referred to as “power error” hereinafter) felt by the eyes will change compared with the case where these lenses is fitted into a spectacle frame having no or vary small front angle, the spectacle wearer will feel severe discomfort. To solve such problem, the following methods have been conventionally used: (1) increasing the curve of the lenses in order to reduce the prismatic effect felt by the eyes caused due to the lenses being tilted to the outside; (2) adding a correction prism to the lenses in order to offset the extra prismatic effect caused by the front line-of-sight; (3) correcting the shape of the back surfaces (concave surfaces) of the lenses in order to remove the astigmatism and the mean power error felt by the eyes when viewing objects in front line-of-sight; and (4) forming the back surfaces of the lenses into an aspherical shape so as to reduce the astigmatism and the mean power error felt by the eyes in the area excluding the front line-of-sight (see, for example, Patent document 1). By using these methods, the discomfort felt by the spectacle wearer can be reduced to some extent.